The base of cermet alloys used for tools are usually titanium carbide, which has nitrogen content (hereinafter referred to as Ti(C,N)). The Ti (C, N) base cermet alloy is superior to conventional titanium carbide (hereinafter referred to as TiC) base cermet alloy in many properties such as room temperature strength, oxidation resistance and machinability.
Both the TiC based and the Ti(C,N) based cermet alloys have a hard phase comprising particles in a composite core/shell structure where the core (TiC for the former and Ti(C,N) for the latter) is surrounded by the peripheral structure of (Ti, Mo)C and (Ti, Mo)(C, N), respectively. The Ti(C,N) base alloy has a finer particle size under the effect of nitrogen content, which realizes improved toughness.
The Ti(C,N) base cermet alloy is also known for having an excellent high-temperature strength.
This advantage attributes to the bonding phase having more solid solution of Mo, which suppresses dynamic restoration of the phase. The mechanism where Mo solid solution is formed in the bonding phase is supposed that Ti, which is supersaturated from Ti(C,N) in denitrification during vacuum sintering, forms a carbide together with C from Mo.sub.2 C with the remaining Mo making solid solution in the bonding phase.
Recently, wet machining is often adopted for better environment at machining sites. In such cases, it is required that the tool material has higher hardness and toughness, as well as excellent heat resistance so as to prevent property degradation under the effect of the heat during machining and cooling with machining fluid.